1. Field of the Invention
The present invention relates to a production method of a base plate for a disk drive, a base plate for a disk drive, and a disk drive provided with the base plate.
2. Description of Related Art
In general, a disk drive such as a hard disk drive, which may be used in an electronic device, includes a base plate as a main part, and the base plate is formed with a recess and an open portion. The recess accommodates a magnetic disk (a recording medium), a spindle motor, a head stack assembly including a magnetic head, and the like. The open portion is sealed by a top cover. The base plate has a back side, that is, a surface at the side opposite to the recess, to which a control circuit board is fixed. The control circuit board is mounted with control circuits for the spindle motor, the magnetic head, an actuator, and the like, and an interface circuit for the electronic device.
Usually, the base plate is made by aluminum die casting which allows mass production at low cost. The base plate made by aluminum die casting is entirely coated with a resin film by electrodeposition so as to protect the surface and to prevent corrosion and occurrence of microscopic material causing contamination (hereinafter called “particles”). For example, a technique is disclosed in Japanese Unexamined Patent Application Laid-open No. 2008-27540. In this technique, after a base plate is machined, the base plate is cleaned and coated with a resin film having, for example, a thickness of not more than 50 μm. The resin film can be formed by electrodeposition coating.
The film formed by the electrodeposition coating tends to have a large thickness. Therefore, finishing is performed by machining the portions in which a high dimensional accuracy is required, such as a motor mounting portion, a mounting portion for a pivot bearing of the head stack assembly, etc. In addition, screw holes for fixing the top cover and the like are also formed by machining after the electrodeposition coating. Thus, the machining is essential after the electrodeposition coating. Accordingly, a conventional base plate has been used in a condition in which aluminum surface is exposed at machined portions.
In the machined portions with exposed aluminum surface, minute particles of approximately 0.1 micrometer to several micrometers in size adhere on the surface. These particles cannot be completely removed even by cleaning and they partially remain on the machined surface. On the other hand, the gap between the magnetic head and the magnetic disk has been extremely reduced to not more than 10 nm due to a recent trend toward increasing capacity and reducing dimensions. Therefore, failure of disk drive due to the collision of the magnetic head with the remaining particles adhered to the surface of the magnetic disk has occurred and become a problem.
Another technique is disclosed in Japanese Unexamined Patent Application Laid-open No. 2010-225207. In this technique, a base plate has an outer circumference provided with a circumferential wall made of plastic, thereby reducing generation of particles. The circumferential wall made of plastic does not oxidize and thereby does not generate particles.